GEPHE SUMMARY
Gephebase Gene
Entry Status
Published
GepheID
GP00001912
Main curator
Courtier
PHENOTYPIC CHANGE
Trait Category
Trait State in Taxon A
presence of stomach and gastric acid production
Trait State in Taxon B
loss of stomach and no gastric acid production
Ancestral State
Taxon A
Taxonomic Status
Taxon A
Common Name
gray short-tailed opossum
Synonyms
gray short-tailed opossum; Monodelphis domesticus
Rank
species
Lineage
Show more ... iata; Vertebrata; Gnathostomata; Teleostomi; Euteleostomi; Sarcopterygii; Dipnotetrapodomorpha; Tetrapoda; Amniota; Mammalia; Theria; Metatheria; Didelphimorphia; Didelphidae; Didelphinae; Monodelphis
NCBI Taxonomy ID
is Taxon A an Infraspecies?
No
Taxon B
Common Name
platypus
Synonyms
platypus; duck-billed platypus; duckbill platypus; Ornythorhynchus anatinus
Rank
species
Lineage
Show more ... Chordata; Craniata; Vertebrata; Gnathostomata; Teleostomi; Euteleostomi; Sarcopterygii; Dipnotetrapodomorpha; Tetrapoda; Amniota; Mammalia; Prototheria; Monotremata; Ornithorhynchidae; Ornithorhynchus
NCBI Taxonomy ID
is Taxon B an Infraspecies?
No
GENOTYPIC CHANGE
UniProtKB
Homo sapiens
GenebankID or UniProtKB
Presumptive Null
Yes
Molecular Type
Aberration Type
Deletion Size
10-100 kb
Molecular Details of the Mutation
Absence of the gene in the genome sequence - high synteny
Experimental Evidence
Authors
Ordoñez GR; Hillier LW; Warren WC; Grützner F; López-Otín C; Puente XS
Abstract
The duck-billed platypus (Ornithorhynchus anatinus) belongs to the mammalian subclass Prototheria, which diverged from the Theria line early in mammalian evolution. The platypus genome sequence provides a unique opportunity to illuminate some aspects of the biology and evolution of these animals.

We show that several genes implicated in food digestion in the stomach have been deleted or inactivated in platypus. Comparison with other vertebrate genomes revealed that the main genes implicated in the formation and activity of gastric juice have been lost in platypus. These include the aspartyl proteases pepsinogen A and pepsinogens B/C, the hydrochloric acid secretion stimulatory hormone gastrin, and the alpha subunit of the gastric H+/K+-ATPase. Other genes implicated in gastric functions, such as the beta subunit of the H+/K+-ATPase and the aspartyl protease cathepsin E, have been inactivated because of the acquisition of loss-of-function mutations. All of these genes are highly conserved in vertebrates, reflecting a unique pattern of evolution in the platypus genome not previously seen in other mammalian genomes.

The observed loss of genes involved in gastric functions might be responsible for the anatomical and physiological differences in gastrointestinal tract between monotremes and other vertebrates, including small size, lack of glands, and high pH of the monotreme stomach. This study contributes to a better understanding of the mechanisms that underlie the evolution of the platypus genome, might extend the less-is-more evolutionary model to monotremes, and provides novel insights into the importance of gene loss events during mammalian evolution.
Additional References
RELATED GEPHE
COMMENTS
lack of acid secretion in the platypus stomach - this is a characteristic feature of monotremes whose gastric juice is above pH 6
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